Various solid materials used in road construction were analyzed using a handheld Raman spectrometer. The investigated materials are commonly used pigments and resins such as CaCO3, TiO2, and DEGALAN®. The measured spectra differed remarkably from each other. To evaluate the main differences in the chemical structures, the peaks of the different spectra were assigned to the functional groups causing them.
Different materials such as paints, (white) pigments, and resins are commonly used in the construction of roads. Together with glass beads (used for night-visible road marking) and various other materials, they help us to get safely from A to B.
In this study, different roadmaking materials were analyzed using the Mira M-1 handheld Raman analyzer. The gathered spectra were compared with each other to see the main differences in the functional groups. The analysis proved that Mira M-1 is suited for the differentiation of such materials.
All spectra were measured using the Mira M-1 Raman spectrometer in auto-acquisition mode, i.e., integration times were determined automatically. A laser wavelength of 785 nm and the Orbital-Raster-Scan (ORS) technique were applied. The measurements were done in small sample vials with the vial holder adapter.
The following samples were investigated:
- Chalk (CaCO3)
- Titanium dioxide (TiO2)
- EPONAC® resin
- TP resin
- Pigment yellow
- Pigment blue
- Pgiment red
- DEGALAN® resin
The measurement of calcium carbonate furnished a clear spectrum with two main peaks at 712 cm-1 (symmetric O–C–O bending vibration) and 1087 cm-1 (symmetric stretching vibration).
Looking at the titanium dioxide spectrum, one can see two main peaks which give information on the present crystal modification (rutile or anatase). Two peaks represent rutile, while three peaks are typical for anatase because of its crystal symmetry.
Both peaks are symmetric stretching vibrations and belong to O–Ti–O (446 cm-1) and Ti–O (609 cm-1). In the case of anatase, the peak at 446 cm-1 is split in two. This makes it easy to differentiate between rutile and anatase.
A glance at the spectra of typical resins such as EPONAC® or DEGALAN® reveals nicely separated peaks which can be assigned to their corresponding functional groups (see below).
| Peak [cm-1] | Description |
|---|---|
| 640 | Cyclic vibration (para-substituted benzene) |
| 819 | C–H bending vibration (para-substituted benzene) |
| 1000 | Various C–C stretching vibrations |
| 1113 | C–OH stretching vibration |
| 1189 | C–(CH3)2 stretching vibration |
| 1231 | C–O |
| 1248 | C–H (benzene) |
| 1298 | –CH2– twisting vibration |
| 1461 | –CH2– bending vibration |
| 1609 | C=C |
The peaks are very characteristic for para-substituted benzene and confirm that EPONAC® is a copolymer of bisphenol A (BPA) and another component.
When comparing the EPONAC® spectrum with the DEGALAN® spectrum (see Figure 5), it is obvious that the peak of the benzene at 1600 cm-1 is missing. The peak around 1700 cm-1, together with the peaks slightly below and above 1200 cm-1, is characteristic for carbonyl groups. In addition to that, the C–C peaks are more distinct for EPONAC® than for DEGALAN®.
| Peak [cm-1] | Description |
|---|---|
| 599 | –COO bending vibration |
| 814 | Propionate bending vibration |
| 843 | C–CH3 stretching vibration |
| 965 | C–C stretching vibration |
| 1065 | C–COO stretching vibration |
| 1125 | C–O |
| 1234 | C–O |
| 1308 | –CH2– twisting vibration |
| 1452 | –CH2– bending vibration |
| 1728 | C=O carbonyl group, ester |
Using these differences, it is easy to discriminate between the resins and also between resins and pigments (see Figure 6).
Because of the great differences in their spectra, handheld Raman spectroscopy is ideally suited for the analysis of materials used in road construction. The investigation of the spectra showed that there are significant differences in the functional groups of the materials, thus allowing the identification with handheld Raman systems such as Mira M-1.
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